System for shutting-off and relieving the pressure in a liquid supply line

Abstract

Shutting off a liquid supply line ( 2, 3 ) intended to convey foam precursors into a polyurethane foam mixing and dispensing gun, gives a better result when a system for shutting off and relieving the pressure is inserted in said supply line. This system enables to annul the pressure at the closed mouth of the gun by relieving the pressure in the supply line ( 2, 3 ).

What is claimed is:  
     
       1. A shut-off and pressure-relief device for controlling a supply of foam precursors into a foam mixing and dispensing means, said device comprising a first and a second supply unit, each having a first input for inputting one of said precursors into said supply unit, and a first output connected to a mixing chamber, each supply unit further comprises a piston type pressure pump, having an expansion and a pressure chamber, and a piston arranged to be moved within said pressure and expansion chambers, said pressure chamber being connected to said first input by means of a first duct and to said mixing chamber by means of a second duct, a first head of said piston being provided to be driven into said pressure chamber by means of a driving power supplied on said piston within said expansion chamber so that when said driving power is supplied, said first head is moved within said pressure chamber so as to enable the latter to be filled with one of said foam precursors through said first duct until said first head reaches a position in which said first head opens a passage for said foam precursor from said pressure chamber to said mixing chamber through said second duct. 
     
     
       2. A shut-off and pressure-relief device as claimed in  claim 1 , wherein each supply unit comprises a spring applied around said piston for returning said first head after it has reached said position in which said first head opens said passage for said foam precursor from said pressure chamber to said mixing chamber and after said driving power stops to be applied. 
     
     
       3. A shut-off and pressure-relief device as claimed in  claim 1  or  2 , wherein said supply units are mounted into said dispensing means. 
     
     
       4. A shut-off and pressure-relief device as claimed in  claim 1  or  2 , wherein said supplied driving power is provided by an hydraulic fluid and each supply unit comprises a third duct ending in said expansion chamber for supplying said hydraulic fluid into said expansion chamber. 
     
     
       5. A shut-off and pressure-relief device as claimed in  claim 1  or  2 , wherein said pressure and expansion chambers are separated by means of an O ring wrapped around a rod of said piston. 
     
     
       6. A shut-off and pressure-relief device as claimed in  claim 2 , wherein said spring is arranged within said expansion chamber. 
     
     
       7. A shut-off and pressure-relief device as claimed in  claim 6 , wherein said piston has a second head opposite to said first head and arranged within said expansion chamber and wherein said spring and said third duct are arranged on opposite sides of said second head.